Add a HISTORY file for unstable
Add a HISTORY file for unstable

Note: I tried to reconstruct some history back
to 5.3.4, but it's not complete.

Please merge to v6.0

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket